The Treatment of Lead-Exposed Children (TLC) clinical trial was carried out in four large urban pediatric departments. The study was designed to test the hypothesis that children with moderate blood lead concentrations who were treated with succimer would have higher scores than placebo treated children on a range of tests measuring cognitive and behavioral development three years after treatment. TLC randomized 384 children to placebo and 396 to succimer between August 1994, and January, 1997. Recognizing that the most important effects of early lead exposure are difficult to assess prior to school age, TLC-Plus is designed to assess the long-term developmental benefits of oral chelation therapy with succimer. The study's principal aim is to determine whether succimer is effective in ameliorating the adverse impact of early lead toxicity on neuropsychological functioning behavior and social adjustment. A state of the art, efficient assessment battery will be administered to TLC-Plus subjects at all Clinical Centers in two sessions following their seventh birthday. At this age, a wider and more differentiated range of abilities can be examined, scores on psychometric measures are more precise and reliable, and early academic performance and social functioning outside of the home environment can be evaluated. Assessments of psychometric, psycho educational, social-adaptive, and neurological functioning will be made Instruments tapping these domains will be administered to TLC subjects when they attain 7 and 7.5 years of age. Intent-to-treat data analyses will examine the impact of treatment on these domains using analysis of covariance and repeated measures methods.